Sealing structure for a liquid storage vessel having a floating head

ABSTRACT

A sealing structure for use in a liquid storage vessel such as an oil storage tank having a floating head or roof, the sealing structure comprising a hollow resilient core of generally loop form, which core has a substantially arcuate cross section and is allowed to contract or expand in cross section when subjected to stress when the floating head is moved relative to the body of the vessel.

United States Patent Okamoto Dec. 16, 1975 SEALING STRUCTURE FOR ALIQUID 3,043,468 7/1962 Homer, Jr. 220/26 s STORAGE VESSEL HAVING A FLO3,119,511 l/l964 Giannini 4 220/26 S HEAD 3,135,415 6/1964 Fino 220/26 S3,136,444 6/1964 Moyer 220/26 S [75] Inventor: Chikashi Okamoto,Yokkaichi, 3,228,702 l/l966 Ulm et al. 277/343 X Japan 3,333,725 8/1967Hirata et al 220/26 S 3,338,454 8/1967 Nelson 220/26 S Asslgneel PPKakoklcflmpany, Llmlted, 3,372,831 3/1968 Daniels et 31.... 220/26 5Tokyo, Japan 3,373,891 3/1968 Kidd 1 220/26 S Filed: Dec. 1973 3,795,3393/1974 Barbier 220/26 S PP 423,532 Primary Examiner-John PetrakesAttorney, Agent, or Firm-Haseltine, Lake & Waters [30] ForeignApplication Priority Data Feb. 14, 1973 Japan 48-17497 ABSTRACT Asealing structure for use in a liquid storage vessel [52] U-S. Cl.220/226; 220/2l6;.220/222; Such as an oil Storage tank having a floatinghead or 51 I C1 277/226 277/229 roof, the sealing structure comprising ahollow resil- E A :33 21 2 22 35 ient core of generally loop form, whichcore has a sub- 1 Searc stantlally arcuate cross section and is allowedto con- 220} 216-227; 277/ 232 tract or expand in cross section whensubjected to stress when the floatin head is moved relative to the [56]Reierences C'ted body of the vessel. g

UNITED STATES PATENTS 2,910,209 10/1959 Nelson 277/226 x 6 Chums 4 DmwmgUS. Patent Dec. 16, 1975 SEALING STRUCTURE FOR A LIQUID STORAGE VESSELHAVING A FLOATING HEAD The present invention relates generally to aliquid storage vessel with an unsecured top and specifically to anaboveground gas-tight oil storage tank having a floating head or roof.More specifically, the present invention is concerned with a sealingarrangement to be used in the oil storage tank of the particular typefor hermetically sealing the tank between the tank body and the floatinghead.

Gas-tightness and durability are essentials of oil storage tanks andaccordingly the principal requirements for the sealing arrangement ofthe oil storage tank of the described type are a uniform and constantpressure between the tank body and the floating head, responsiveness tothe movement of the floating head relative to the tank body, andresistance to wear and abrasion resulting primarily from the frictionbetween the contact surfaces of the tank body and the sealing structure.If the sealing pressure between the tank body and the floating head isdeficient, gaps may be produced between the inner peripheral surface ofthe tank body and the rim of the head although the sealing structure maybe subject to lesser wear and abrasion that will result in a prolongedservice life of the sealing structure. Oil vapor will therefore escapeand, in some cases, oil itself may leak from the tank through such gaps,causing not only a considerable amount of loss of the stored oil but thedanger of a conflagration or explosion if a spark happens to be producedin the neighborhood of the leaks as in the event of an earthquake. If,conversely, the sealing pressure is excessive, complete sealing of thetank may be achieved and the relative movement between the tank body andthe floating head may be accommodated to satisfactorily by the sealingarrangement but the wear and abrasion of the sealing structure will beaccelerated resulting in a shortened service life of the sealingarrangement. Other important requirements for the sealing arrangementfor the oil storage tank of the described type include: resistance to anundue stress which may be imparted to the sealing structure as a resultof upward and downward movements or sways of the floating head;configurations adapted to match the geometry of the tank and to bereadily installed into a working position; and simple, economical androbust construction.

A variety of sealing arrangements have thus far been proposed with aview to meeting these requirements, but none of the arrangements hassucceeded in satisfying all of such requirements. The present inventioncontempletes provision of an improved sealing structure which is capableof meeting all the above mentioned requirements.

It is, accordingly, an object of the present invention to provide animproved sealing structure for use in a liquid storage vessel having afloating head so as to achieve complete sealing between the body and thefloating head of the vessel.

It is another object of the invention to provide an improved sealingstructure for a liquid storage vessel of the described type wherein thesealing pressure exerted between the tank and the floating head of thevessel is maintained satisfactorily uniform and constant substantiallyirrespective of the position of the floating head relative to the bodyof the vessel.

It is still another object of the invention to provide an improvedsealing structure for use in a liquid storage vessel of the describedtype which structure is highly responsive to upward and downwardmovements or sways of the floating head relative to the body of thevessel so that the floating head is at all times maintained in abalanced position relative to the vessel body.

It is still another object of the invention to provide an improvedsealing structure for use in the liquid storage vessel of the describedtype, the sealing structure having sufficient resistance to wear andabrasion that will assure a prolonged service life of the sealingstructure.

It is still another object of the invention to provide an improvedsealing structure for a liquid storage vessel of the described type,wherein the sealing structure is sufficiently resistant to undue stresswhich may be imparted to the structure as a result of upward anddownward movements of the floating head relative to the body of thevessel.

It is still another object of the invention to provide an improvedsealing structure for use in a liquid storage vessel of the describedtype, which structure is adapted to be readily installed in a workingposition in the vessel.

It is still another object of the invention to provide an improvedsealing structure which is adapted for use specifically in a liquidstorage vessel of the described type and which is simple and robust inconstruction and economical to manufacture.

It is, thus, a general object of the present invention to provide anaboveground gas-tight liquid storage vessel having a floating head whichis hermetically sealed from the body of the vessel by an improvedsealing arrangement adapted to provide increased gastightness anddurability of the storage vessel as a whole and accordingly enhancedassurance of safety required under any local regulations for theprevention of a conflagration or explosion of the vessel in the event ofan earthquake or any other disaster.

In accordance with the present invention, these and other objects areaccomplished in a sealing structure comprising a resilient coreincluding an elongated inner core member having a substantiallyrectangular cross section and substantially parallel inner and outerlongitudinal surfaces and an elongated outer core member having asubstantially arcuate cross section projecting outwardly away from theouter longitudinal surface of the inner core member and substantiallyparallel upper and lower longitudinal ends respectively secured to theupper and lower longitudinal ends of the outer longitudinal surface ofthe inner core member, the outer core member being initially fromed as asubstantially flat strip and being thereafter forcibly deformed into aconfiguration having the aforesaid arcuate cross section, and a flexiblecovering member which hermetically encloses the core therewithin andwhich is adapted for being slidably pressed partly between the innerlongitudinal surface of the inner core member and an outer peripheralsurface of the floating head and partly between the projecting outerlongitudinal surface of the outer core member and and inner peripheralsurface of the liquid storage vessel. The core may further include upperand lower resilient elongated members having respective upper and lowerlongitudinal ends respectively secured to upper and lower longitudinalportions of the outer longitudinal surface of the inner core member andrespective outer longitudinal surfaces which are secured at their upperand lower end portions to upper and lower end portions, respectively, ofthe inner longitudinal surface of the outer core member, the resilientelongated members having respective lower and upper free longitudinalend portions which are spaced apart from each other and which are atleast in part resiliently forced against the inner longitudinal surfaceof the outer core member. By preference, the core may still furtherinclude upper and lower intermediate strips of resilient material whichare at least partly in slidable contact between the upper and lowerlongitudinal surface of the inner core member and outer surfaces of thelower and upper free longitudinal end portions of the upper and lowerresilient elongated members, respectively, and which have respectiveupper and lower longitudinal end portions respectively secured to theweld between the outer core member and the upper resilient elongatedmember and the weld between the outer core member and the lowerresilient elongated member.

The inner and outer core members and the upper and lower resilientelongated members are preferably formed of a foam thermoplastic resinsuch As, for example, polyurethane while the upper and lowerintermediate strips may be formed of any one of the known thermoplasticresins.

The features and advantages of the sealing structure according to thepresent invention will become more apparent from the followingdescription of the invention taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a fragmentary perspective view partially in cross section, ofa core forming part of a preferred embodiment of the sealing structureaccording to the present invention;

FIG. 2 is a cross sectional view of the embodiments of the sealingstructure which is in a condition installed in an oil storage tankhaving a floating head;

FIG. 3 is a fragmentary cross sectional view of the core of the sealingstructure in the installed condition; and

FIG. 4 is a fragmentary perspective view showing partially in crosssection, the configuration of part of the core of the sealing structurewhich is spread out into the form of an endless belting so as to show aprocess which may be used to obtain the formation illustrated in FIG. 1.

Reference will now be made to the drawings, first to FIG. 1 in which thecore forming part of the sealing structure according to the presentinvention is shown to be in a free or relaxed condition. As illustrated,the core, designated in its entirety by reference numeral 10, includesan inner elongated core member 12 and an elongated outer core member 14.The inner core member 12 has a substantially rectangular cross sectionand accordingly substantially parallel inner and outer surfaces. Theouter core member 14, on the other hand,

extends along the outer surface of the inner core memmember 12, asindicated at P and P in FIG. 1. The core 10 further comprises a pair of,upper and lower, internal wedge members 18 and 18 which extend alongupper and lower portions, respectively, of the inner surface of theouter core member 14. The upper internal wedge member 18 is bonded orotherwise secured at an upper end portion of its outer surface to anupper end portion of the inner surface of the outer core member 14 asindicated at Q and is further secured at its upper longitudinal end tothe upper end portion of the inner surface of the inner core member 12as indicated at R. Likewise, the lower internal wedge member 18' issecured at a lower longitudinal end portion of its outer surface to alower end portion of the inner peripheral surface of the outer coremember 14 as indicated at Q and is further secured at its lowerlongitudinal end to the lower end portion of the inner surface of theinner core member 12 as indicated at R. These upper and lower internalwedge members 18 and 18 have lower and upper free end portions,respectively, which are at least in part resiliently forced against theinner surface of the outer core member 14 and which are spaced apartfrom each other in vertical directions By preference, the lower andupper free end portions of the upper and lower internal wedge members 18and 18, respectively, are reduced in thickness toward their ends so thateach of the wedge members 18 and 18 has a generally wedge-shaped crosssection which is curved over the inner surface of the outer core member14 as shown. The inner and outer core members 12 and 14 and the internalwedge members 18 and 18' are formed of light-weight resilient plasticmaterial such as foamed thermoplastic material a typical example ofwhich is polyurethane foam.

The core 10 having the construction above described may be placed in useas is but, for the reasons to be explained, the core may furthercomprise, as shown, a pair of, upper and lower, intermediate strips 20and 20, respectively, of a flexible plastic material which is preferablyheterogeneous to the material forming the members 12, 14, 18 and 18. Theupper intermediate strip 20 is interposed between the upper portion ofthe inner surface of the outer core member 14 and the outer surface ofthe free end portion of the upper inter nal wedge member 18 and isbonded or otherwise secured at its upper longitudinal end to the weldline between the outer core member 14 and the upper internal wedgemember 18. Likewise, the lower intermediate strip 20 is interposedbetween the lower portion of the inner surface of the outer core member14 and the outer surface of the free end portion of the lower internalwedge member 18 and is bonded or otherwise secured at its lowerlongitudinal end to the weld line between the outer core member 14 andthe lower internal wedge member 18. The intermediate strips 20 and 20are thus partly in slidable contact between the inner surface of theouter core member 14 and the outer surfaces of the free end portions ofthe upper and lower strips 20 & 20, respectively intermediate strips.The 20 and 20' are herein shown as projecting beyond the free ends ofthe internal wedge members 18 and 18, respectively, but, where desired,they may be substantially coextensive with or concealed benind theinternal wedge members 18 and 18.

I FIG. 2 illustrates a sealing structure incorporating the core 10having the above described construction. The core 10 is enclosed orwrapped in flexible covering members 22 and 22' which are securelyconnected together by suitable" fastening means 24 which are shown ascomprising a clamping nut 24a and a'bolt 24b. The covering members 22and 22' are usually formed of rubber coated cloth. 1

The sealing structure thus arranged is mounted on an oil storage'ta'nkwhich is shown in phantom in FIG. 2 as consisting of 'a tank body 26 anda'floating head 28. The tank body 26 stores therein oil or anyotherliquid of, usually, an inflammable property'and the floating head28 floats on the surface'of oil; Topermit movement of the floatinghead'28 relative tothe tank body 26, the head 28 has a rim 28a which isso-sized as to provide an appropriate allowance'between the innerperipheral surface of the tank body 26 and the rim 28a of the head 28.The core of the sealing structure should therefore be so arranged that,when the core is in a free or relaxed condition which is'free fromstress, the overall widthof the core or, in other words, the distancebetween the inner'surface of the inner core member 12 and the outer endof theouter-core member 14 is significantly larger than the amount ofclearance between tank body 26 and the floating head 28. When thesealing structure is to be placed in a working position,the core.10complete with the covering members 22 and 22 is forced between the innerperipheral surface of the tank body 26 and the rim 28a of the floatinghead 28 so that the outer core member 14 is caused to contract towardthe outer surface of the inner core member 12 against the resiliency ofthe material forming the loop portion 14. The outer surface of the outercore member 14 is consequently partly flattened and is tightly pressedagainst the inner peripheral surface of the tank body 26 through thecovering member 22 while the inner surface of the inner core member 12is fast on the rim 28a of the floating head 28 through the othercovering member 22'. Under these conditions, the upper and lowerinternal wedge members 18 and 18 are tightly forced toward the internalsurfaces of the outer core member 14 across the upper and lowerintermediate strips and 20, respectively, thereby adding to the forcesthat act to press the outer core member 14 against the inner peripheralsurface of the tank body 26.

When the outer core member 14 has its top portion flattened andcontracted toward the inner surface of the inner core member 12, theupper and lower end portions of the outer core member 14 are deformed tocreate certain angles 0 between the outer surfaces of the particularportions of the outer core member 14 and horizontal planes at the upperand lower ends of the inner core member 12 as seen in FIG. 3 so that theupper and lower portions of the outer core member 14 are forcefullyurged upwardly and downwardly, respectively, as indicated by arrows F inFIG. 3. The forces F will provide sufficient resistance to upward anddownward deformation of the core and to bending or compressive stressesimparted to the core as a result of the movement of the floating head 28relative to the tank body 26. Such resistance will be reinforced by theforces which are exerted by the upper and lower internal wedge members18 and 18' which press the upper and lower portions of the outer coremember 14 partly upwardly and downwardly respectively, and partlyoutwardly of the inner core member 12. Substantially uniform sealingpressure is achieved in this manner at all times by the core 10irrespective of the position of the floating head 28 relative to thetank body 26.

When the core 10 is in the contracted condition above described andespecially when the core is subjected to stresses created by themovement of the floating head 28 relative to the tank body 26, the freeend portions ofthe internal wedge members 18 and 18 will be movedrelative to the outer core member 14. Such movement of the internalwedge members 18 and 18 is facilitated by means of the upper and lowerintermediate strips 20 and 20 which are in slidable engagement with boththe inner surface of the outer core member 14 and the outer surfaces ofthe free end portions of the upper and lower internal wedge members 18and 18', respectively. When, thus, the outer core member 14 is deformedunder stress, the inner surface of the outer core member 14 and theouter surfaces of the internal wedge members 18 and 18' are moved inopposed directions relative to the intermediate strips 20 and 20' and,since, the wedge members 18 and 18' are urged against the intermediatestrips 20 and 20', the inner surface of the outer core member 14 and theouter surfaces of the free end portions of the internal wedge members 18and 18 are caused to-slide on the opposite surfaces of the intermediatestrips 20 and 20', respectiv ely. The outer core'member 14 is in thismanner prevented from being subjected'to undue stresses when theco'remember 14 is moved or deformed relative to the internal wedge members 18and 18.

Members 12, 14, 18 and 18' are first formed separately each in a flatstrip' form and are thereafter secured to each other, in a mannerillustrated in FIG. 4. The outer core member 14 of flat strip form haswidth which is so selected to provide a desired radius of ourvature whendeformed into a configuration having an arcuate cross section shown inFIG. 1. A pair of wedge members 18 and 18 each of the flat strip formare then secured at Q and Q, respectively, to the upper and lowerlongitudinal end portions of the inner surface of the outer core member14. The internal wedge members l8 and 18 have free end portions whichare reduced in thickness toward their respective ends and which areappreciably spaced apart from the inner surface of the outer core member14 as illustrated. A pair of relatively thin strips 20 and 20' are theninterposed between the inner surface of the outer core member 14 and theouter surfaces of the respective free end portions of the wedge members18 and 18', respectively. The strips 20 and 20 are secured to the weldsbetween the outer core member 14 and the wedge members 18 and 18 so asto be loosely sandwiched between the ring-shaped member 14 and the freeend portions of the wedge-shaped members 18 and 18. The outer coremember 14 complete with the wedge members 18 and 18 and the strips 20and 20 attached thereto is then forcibly deformed outwardly into aconfiguration having a generally arcuate cross section and the outercore member 14 and the wedge members, 18 and 18 are secured at theirrespective upper and lower edges to upper and lower longitudinal endportions of an outer surface of an inner core member 12.

What is claimed is:

l. A sealing structure for use in a liquid storage vessel having afloating head, said sealing structure comprising a core including anelongated inner core member of elastic material having a substantiallyrectangular cross section and substantially parallel inner and outerlongitudinal surfaces and an elongated outer core member of elasticmaterial having a substantially arcuate cross section projectingoutwardly away from the outer longitudinal surface of the inner coremember, said outer core member having substantially parallel upper andlower longitudinal ends respectively secured to the upper and lowerlongitudinal ends of the outer longitudinal surface of the inner coremember to form a continuous cavity throughout the length of said core,said outer core member being initially formed separately from said innercore member as a substantially flat elongated strip and being thereafterforcibly deformed into a configuration having said arcuate crosssection, and a flexible covering member hermetically enclosing said coretherewithin and slidably pressed between the inner longitudinal surfaceof said inner core member and an outer peripheral surface of saidfloating head and partly between the projecting outer longitudinalsurface of said outer core member and an inner peripheral surface ofsaid liquid storage vessel.

2. A sealing structure as claimed in claim 1, in which said core furtherincludes upper and lower resilient elongated members having respectiveupper and lower longitudinal ends respectively secured to upper andlower longitudinal portions of the outer longitudinal surface of saidinner core member and respective outer longitudinal surfaces which aresecured at their upper and lower end portions to upper and lower endportions, respectively, of the inner longitudinal surface of said outercore member, said resilient elongated members having respective lowerand upper free longitudinal end portions which are spaced apart fromeach 8 other and which are at least in part resiliently forced againstthe inner longitudinal surface of said outer core member.

3. A sealing structure as claimed in claim 2, in which said core furtherincludes upper and lower intermediate strips of resilient material whichare at least partly in slidable contact between the upper and lowerlongitudinal portions, respectively, of the inner longitudinal surfaceof said inner core member and outer surfaces of said lower and upperfree longitudinal end portions of said upper and lower resilientelongated members, respectively, and which have respective upper andlower longitudinal end portions respectively secured to the junctionbetween the outer core member and said upper resilient elongated memberand the junction between the outer core member and said lower resilientelongated member.

4. A sealing structure as claimed in claim 2 in which the free endportions of said upper and lower resilient elongated members are reducedin thickness toward their respective lower and upper ends to form awedgeshape.

5. A sealing structure as claimed in claim 2 in which said inner andouter core members and said upper and lower elongated members are formedof foam thermoplastic material.

6. A sealing structure as claimed in claim 5 in which said foamthermoplastic material is polyurethane foam.

1. A sealing structure for use in a liquid storage vessel having afloating head, said sealing structure comprising a core including anelongated inner core member of elastic material having a substantiallyrectangular cross section and substantially parallel inner and outerlongitudinal surfaces and an elongated outer core member of elasticmaterial having a substantially arcuate cross section projectingoutwardly away from the outer longitudinal surface of the inner coremember, said outer core member having substantially parallel upper andlower longitudinal ends respectively secured to the upper and lowerlongitudinal ends of the outer longitudinal surface of the inner coremember to form a continuous cavity throughout the length of said core,said outer core member being initially formed separately from said innercore member as a substantially flat elongated strip and being thereafterforcibly deformed into a configuration having said arcuate crosssection, and a flexible covering member hermetically enclosing said coretherewithin and slidably pressed between the inner longitudinal surfaceof said inner core member and an outer peripheral surface of saidfloating head and partly between the projecting outer longitudinalsurface of said outer core member and an inner peripheral surface ofsaid liquid storage vessel.
 2. A sealing structure as claimed in claim1, in which said core further includes upper and lower resilientelongated members having respective upper and lower longitudinal endsrespectively secured to upper and lower longitudinal portions of theouter longitudinal surface of said inner core member and respectiveouter longitudinal surfaces which are secured at their upper and lowerend portions to upper and lower end portions, respectively, of the innerlongitudinal surface of said outer core member, said resilient elongatedmembers having respective lower and upper free longitudinal end portionswhich are spaced apart from each other and which are at least in partrEsiliently forced against the inner longitudinal surface of said outercore member.
 3. A sealing structure as claimed in claim 2, in which saidcore further includes upper and lower intermediate strips of resilientmaterial which are at least partly in slidable contact between the upperand lower longitudinal portions, respectively, of the inner longitudinalsurface of said inner core member and outer surfaces of said lower andupper free longitudinal end portions of said upper and lower resilientelongated members, respectively, and which have respective upper andlower longitudinal end portions respectively secured to the junctionbetween the outer core member and said upper resilient elongated memberand the junction between the outer core member and said lower resilientelongated member.
 4. A sealing structure as claimed in claim 2 in whichthe free end portions of said upper and lower resilient elongatedmembers are reduced in thickness toward their respective lower and upperends to form a wedge-shape.
 5. A sealing structure as claimed in claim 2in which said inner and outer core members and said upper and lowerelongated members are formed of foam thermoplastic material.
 6. Asealing structure as claimed in claim 5 in which said foam thermoplasticmaterial is polyurethane foam.